1. Field of the Invention
The present invention relates to an ultrasonic image diagnosing apparatus comprising an ultrasonic probe for transmitting three-dimensionally an ultrasonic wave toward a living body under inspection and receiving an ultrasonic wave reflected by the living body to generate echo data of a three-dimensional region, an image processing means for processing the echo data to produce a three-dimensional image signal, and a display means for displaying a three-dimensional image of the living body.
In almost all ultrasonic image diagnosing apparatuses of the kind mentioned above, ultrasonic echo data representing a number of mutually parallel cross sectional images is processed to generate the three-dimensional image signal and this three-dimensional image signal is supplied to the two-dimensional display means to display a three-dimensional image. It should be noted that the thus displayed three-dimensional image is not a true three-dimensional image, but is a pseudo three-dimensional image. For the sake of simplicity, in the present specification, the pseudo three-dimensional image is called a three-dimensional image.
In a general three-dimensional image processing apparatus for medical use such as the above mentioned ultrasonic image diagnosing apparatus displaying the three-dimensional image, in order to display three-dimensionally a desired object or cavity within the living body, a so-called shading treatment has been widely utilized. As the shading treatment, there have been proposed various methods such as a volume rendering method in which the shading treatment is performed while maintaining the tone or gray scale based on object information which is inherently contained in the echo data, and a surface model method, in which a surface is extracted by converting the tone of echo data into bivalent data with the aid of a constant threshold level and then the shade is applied to the thus extracted surface.
In case of displaying the three-dimensional image of the object, when use is made of the volume rendering method, it is necessary to treat three-dimensional data having tones, and consequently, an amount of data to be processed becomes very large and a treating time is liable to be long. When the surface model method is used, only the bivalent data of the surface is processed, so that the treating time may be reduced, but the tone based on the object information inherent to the echo data is lost. Thus, an accurate diagnosis might not be performed.
In order to overcome the above mentioned problem, in Japanese Patent Application Laid-open Publication Kokai Hei 4-279156, there is proposed an ultrasonic image diagnosing apparatus, in which a surface of an object is displayed to have a tone and a cross section is displayed as a B-mode image having the tone. In this known apparatus, it is necessary to provide a cross section extracting means for extracting cross sectional image data. The process of extracting the cross sectional image data requires a rather long time period. Moreover, this known apparatus has a drawback that the accuracy of the extraction could be hardly improved.
In the known ultrasonic image diagnosing apparatus, the echo data of a number of mutually parallel cross sectional images is obtained by moving an ultrasonic vibrating element along a longitudinal axis of the probe while the ultrasonic vibrating element is rotated or swung about the longitudinal axis. In the present specification, the mutually parallel cross sectional images are termed lateral cross sectional images, and a longitudinal cross sectional image which is perpendicular to the lateral cross sectional image is derived from the echo data of a number of lateral cross sectional images by the data processing. It is apparent that when the longitudinal cross sectional image is derived after the echo data of all the lateral cross sectional images has been picked-up and stored, the data processing becomes very complicated and requires a relatively long time. In order to avoid such a problem, Japanese Patent Application Kokai Hei 5-15538 has proposed another known apparatus in which both the lateral cross sectional image and longitudinal cross sectional image are displayed simultaneously. However, in this apparatus, a desired area to be inspected might be removed from the longitudinal cross section due to a movement of a living body. As a result, it is uncertain whether a good image for diagnosis can be obtained or not.
In the above mentioned diagnosing apparatus displaying the ultrasonic three-dimensional image, the living body is scanned with the ultrasonic wave in a three-dimensional manner. In Japanese Patent Application Laid-open Publication Kokai Hei 2-265536, there is disclosed an ultrasonic diagnosing apparatus. As shown in FIG. 1, within an ultrasonic probe 101, an ultrasonic vibrating element 102 is rotated by means of a shaft 103 to effect the radial scan, and at the same time the ultrasonic vibrating element 102 is linearly moved in a direction parallel with a longitudinal axis of the ultrasonic probe 101 to perform a linear scan. In this manner, a cavity wall 104 is scanned spirally with the ultrasonic wave and echo data of a three-dimensional region is obtained.
In this known ultrasonic image diagnosing apparatus, the radial scan and linear scan are carried out in synchronism with each other, so that although the scanning speed is changed, a relative speed of these two scans is not changed, and therefore the three-dimensional ultrasonic image can be obtained always under the same condition.
However, the inventors have found that this known apparatus could be further improved in the following points. That is, in order to obtain a useful three-dimensional ultrasonic image for diagnosis, it is necessary to confirm by the radial scan whether or not a desired area of the cavity wall could be actually observed in the three-dimensional image prior to picking-up the echo data of the three-dimensional region. However, in case of performing this confirmation, when a region of interest (ROI) or a desired area 105 to be diagnosed is positioned near an edge of a three-dimensional scan range as illustrated in FIG. 1, only a portion of the desired area 105 denoted by hatchings can be observed. Moreover, even if an operator can operate the ultrasonic probe such that the desired area 105 is correctly positioned at an origin of the linear scan, i.e. a distal end of the ultrasonic probe 101, it is not always possible to obtain a three-dimensional ultrasonic image including the desired area 105, because the origin of the three-dimensional scan is situated at an edge of the scanning range.
In order to avoid the above problem, one might consider to operate manually the ultrasonic probe 1 such that the desired region, i.e. a region of interest 105 is positioned at about a middle point of the linear scan range. However, in this case, a movement of the ultrasonic probe 101 has to be presumed and thus the operation becomes very cumbersome. Moreover, it can not be guaranteed that the region of interest 105 is positively included in the scanning range. It is further considered that once a three-dimensional image has been constructed to confirm that the region of interest is contained in the image, the picking-up or storing of the echo data is initiated. In this case, the construction of the three-dimensional image requires a long time, so that the confirmation also requires a long time.